1. Field of the Invention
The present invention relates to photoelectric switching apparatus, and more particularly to devices for automatically starting and stopping a gas burner, especially a bunsen burner, in response to the shading of a photoelectric control sensor from the ambient light, through the approach of a hand, for example.
2. Description of the Prior Art
The use of bench-type gas burners, especially of so-called bunsen burners, is common in professional laboratories such as dentist's laboratories, for example, as well as in chemical laboratories and various other places, where there is a need for an open gas burner. Generally, such a burner is used intermittently, depending upon the type of work being performed, but the burner has to be ready for immediate ignition in response to a simple control maneuver. For those periods of time, however, during which the burner is not in actual use, it is desirable to have the burner shut down, in order to avoid the unnecessary consumption of large amounts of fuel, and also in order to avoid both the unnecessary consumption of oxygen in the laboratory and the heat development which would result from a continuous operation. In most cases, the actual time of usage of such a burner is a small fraction of the total time of necessary burner readiness.
In an effort to achieve such an automatic starting and stopping action of a gas burner, it has already been suggested in the prior art to provide a shutoff valve in the gas supply line which leads to the burner, which valve is operable mechanically in a simple manner, as for instance through being contacted by the user's hand holding an object to be heated over the gas flame of the burner, the object being a tool, or a test tube, for example.
These known hand-operated gas burners have the short-coming that the user's hand needs to remain steady and in a fixed position, in order to hold the gas valve open, while the same hand also holds the object in question over the flame of the burner. For, as soon as the hand is removed from the gas valve, the latter closes under the action of a closing spring, thereby automatically stopping the burner. This manually operated start-stop burner control device thus does not allow for the user's hand to simultaneously shake the test tube as it is heated, or to rotate a tool or workpiece over the burner flame.